Experimental investigation of the instantaneous flow structure in circulating fluidized bed: Phase characterization and validation

Circulating fluidized beds (CFBs) have been widely used as industrial reactors and the performances rely on the gas-particle contact. In a CFB, particles tend to form dense clusters, sheltering particles from the gas flow. However, in the literature, cluster dimensions and fractions vary up to one order of magnitude, hindering the understanding of CFBs. Recently, it has been found out that different phases were considered as clusters and this circumstance results in the severe variations of cluster properties. In this work, instantaneous solids holdup in a CFB was measured using an optical fiber probe. Then, crest clusters, coalesced particles, trough clusters and dispersed particles were identified in probe signals with the help of images. After that, phases were characterized discriminatively, and phase properties further were validated quantitatively using a high-speed camera. Finally, phases formed by FCC catalysts and glass beads were compared to explore the aggregation mechanism.